The mechanisms by which Treponema pallidum and Borrelia burgdorferi, the agents of syphilis and Lyme disease, respectively, induce inflammation are poorly understood. The applicant's sponsor and his major collaborator have previously shown that the major membrane immunogens of these spirochetal pathogens are covalently modified with lipids and that they are potent monocyte/macrophage activators. These findings support the contention that spirochetal lipoproteins act as major inflammatory mediators in syphilis and Lyme disease. Recent studies by the applicant have established that a novel pathway involving CD14, a GPI-linked protein on the surface of monocytes and macrophages, plays a predominant role in the cellular response to spirochetal lipoproteins and lipopeptides. The overall objective of this proposal is to characterize at the molecular level the binding of CD14 to these spirochetal constituents and to assess the biological relevance of these interactions. This will be accomplished by (a) performing kinetic analyses of CD14-lipoprotein/lipopeptide binding interactions (Specific Aim One), (b) identifying structural elements within CD14 required for lipoprotein/lipopeptide binding and monocyte/macrophage activation (Specific Aim Two), and (c) comparing the inflammatory responses of CD14-expressing and CD14-deficient mice following either intradermal inoculation with lipoproteins/lipopeptides or inoculation with virulent B. burgdorferi. The proposed studies will integrate cellular, molecular, and biophysical methodologies in order to obtain important insights into syphilis and Lyme disease immunopathogenesis and broaden our understanding of how these non-LPS constituents induce deleterious inflammatory responses which ultimately engender clinical manifestations.